Various different types of shoe treads are well known in the art. Usually such treads constitute solid rubber or equivalent resilient material provided with grooves or the like similar to a tire tread, to increase traction and also increase the resiliency and thereby the cushioning effect of the tread. It is also known to provide inner soles for shoes of spongelike material to again provide a cushioning effect.
Usually the solid rubber tread provided on the shoes while exhibiting good anti-skid quality will not really cushion the shoe to the extent often desirable. On the other hand, inner soles of spongy material, while initially providing good comfort, tend to become heated and also packed down after prolonged use, so that the cushioning qualities disappear.
Some of the foregoing disadvantages have been solved by providing soles with a large number of individual air pockets or enclosures which will collapse when walking on the sole. The enclosures themselves have small air openings so that the sole can "breathe" as they are repeatedly compressed and permitted to expand. An example of such structure is in German Pat. No. 474,016 of Feb. 12, 1928. Another example of such structures is shown in U.S. Pat. No. 2,358,342.
While a great improvement is provided with individual air chambers or enclosures, there still can result some problems. More particularly, the geometry of the enclosures is often such that when they collapse under the weight of a person's foot, the resistance force during the collapsing cycle varies enormously. Initially, the air chambers will collapse very easily but as they become more compressed, a greater resistance force is offered. When the chambers are completely collapsed, they form a small lump or nub on the sole which is not particularly comfortable for the wearer.
In view of the foregoing, there still exists a need for an appropriately designed shoe shole providing desired shock absorbing characteristics together with comfort.